A radio control system (hereinafter called “the controlling communication system”), which remotely-controls a controlled object such as a model airplane, a model helicopter or a model automobile in a distant place using radio waves, is arranged to control the controlled object using a control device of an operator and is used in applications such as a hobby application, in which operators compete on the controlling skills such as speed or acrobatic performance, and in industrial equipment applications such as a grass cutter and a crane.
The control device of the controlling communication system is a device for controlling the controlled object and is provided with a transmission unit which transmits a control signal in accordance with the operation performed by an operator. The controlled object is mounted with an object-side communication device which includes a receiving unit for receiving the control signal and a drive control device such as a servo device or a gyroscopic device which maintains the stability of the controlled object, the drive control device being arranged to transmit a drive-control signal from the object-side communication device in accordance with the control signal to perform drive control of a power source such as an engine and a motor, an engine throttle lever and the respective components.
A variety of batteries such as a nickel cadmium battery, a nickel hydride battery and a lithium polymer battery may be used for a power-source battery in the object-side communication device. When the power-supply voltage of the object-side communication device falls below a predetermined value, then the normal communication with the control device may be lost and the controlled object may go out of control, causing runaway or crash of the controlled object.
For this reason, the controlling communication system is provided with a battery failsafe function which notifies to an operator of a decrease in the power-supply voltage of the object-side communication device via an operation of the controlled object. For example, when the power-supply voltage of the object-side communication device falls below a predetermined value, a drive-control signal is outputted to make the angular position of an output shaft of the servo device to be at the predetermined angular position. By doing so, for example if the controlled object is a model airplane, the model airplane circulates. In another example, when the battery failsafe function is applied to a servo device which controls an engine throttle lever, it is controlled to close the engine throttle and minimize the number of revolutions of the engine, for example.
After the battery failsafe function has been implemented, the operator can temporary cancel the battery failsafe function by performing a particular operation, e.g. fully opening the throttle using the control device, so the operator can control the controlled object for a certain period of time such as several tens of seconds. During this period of time the operator retrieves the controlled object. After the certain period of time, the battery failsafe function is implemented again. The operator may arbitrarily cancel the battery failsafe function and retrieve the controlled object before the controlled object becomes out of control due to further power consumption.
An example of a battery failsafe function is shown in Japanese Patent Application Publication No. S61-239796 which discloses a controlling communication system used in a hobby application including an object-side communication device 30 shown in FIG. 4. A control device (not shown) generates and transmits, separately from a control signal, a control signal S for battery failsafe function which controls an engine controlling servo device to stop the engine or to fix the number of revolutions of the engine to the minimum number.
The object-side communication device 30 amplifies and demodulates the signal received at a high-frequency circuit. A decoder 32 distributes the signals to a drive control device (not shown) such as a servo device. At this time, a control signal M for the engine controlling servo device is outputted to a switching circuit 33 together with the control signal S for battery failsafe function.
The switching circuit 33 normally outputs the control signal M; however, when the voltage of a power source 35 detected at a voltage detection circuit 34 falls below a reference voltage value, then the switching circuit 33 outputs to the engine controlling servo device the control signal S for battery failsafe function instead of the control signal M. The operator, once he has checked that the controlled object is being operated by the battery failsafe function, retrieves the controlled object or controls the servo device other than the engine controlling servo device by the control device to evacuate the controlled object to a safe place.
Furthermore, Japan Patent Application Publication No. 2011-78707 discloses a radio control receiver capable of setting a voltage reference value according to the situation and having a memory which stores the set reference voltage value, since the reference voltage value of the power source suitable for implementing the battery failsafe function varies depending on the type of battery and the usage environment.
Conventionally, in the battery failsafe function, the detection time used to determine that the battery voltage is decreased is fixed at about 200 milliseconds. This detection time takes into account the discharge property of the typically-used nickel cadmium battery as well as the time needed to retrieve the controlled object.
Meanwhile in recent years, the controlling communication system has been diversified. For example, introduction of multiple channels has increased the number of servo devices being operated at a time. Furthermore, there have been an increasing number of types of servo devices including a high-power servo device which requires a large amount of current consumption. In addition, various types of batteries having different internal resistance and discharge property are being used. Due to the change in the usage environment of the controlling communication system for the hobby application, the current consumption in the object-side communication device has increased, thus increasing the chance of an instant decrease in voltage of the power source.
In the case of using a high-power servo device in which a large amount of current is consumed by a battery with large inner resistance, depending on the usage environment of the controlling communication system, the conventional detection time for the battery failsafe function may cause the battery failsafe function to activate due to the detection of the instant decrease in voltage, even though there is still sufficient battery capacity left.
Thus, since an operator retrieves the controlled object based on the activation of the battery failsafe function, if the battery failsafe function is activated when there is sufficient battery capacity, the time allowed for the normal control of the controlled object is reduced. Furthermore, there is also a problem that, by charging the battery that has not been fully discharged, the battery life decreases.